The girl in the shower continues. Once again, David Muir. Reporter: As this Florida mother walks the beach, there is little peace. Consumed by the mystery surrounding what happened to her daughter in a hotel just across the street. And while she says police in this small town refused to listen to her, Kelly Osborn's own investigation was heating up. She had three foresnic experts who shared her sneaking suspicion that her daughter was murdered and now the medical examiner who changed the official cause of death from suicide to undetermined. Finally, this mother turned detective had people listening. Her mom believes her daughter was murdered. There's a tremendous amount of pressure that's been applied to, not only those two police officers, but the mayor in Bradenton beach as well. Reporter: Do you think they underestimated this mother? I do, I do. I think they saw her as they described her, just as a grieving mother. Reporter: And now that grieving mother had her sights set on the state's top investigators. Turning to the Florida department of law enforcement, a panel with the power to take another look at the case. And they did. Asking to hear from that first detective who labeled Sheena's death a suicide. Their evidence is presented to them by detective Diaz. He goes over his findings from his investigation. And what does this panel decide? The case needs to be re-opened. State investigators say they will now be looking into this case. Reporter: Was this a hard fought victory? Oh my, yes. Reporter: Finally they were going to investigate your daughter's death. Finally, and why? Why did we have to fight, for four years, four years. Nobody would listen. Reporter: But now they were. Local station fox 13 follows her as she wheels years of her evidence straight through those doors. Justice has not been served. Reporter: And just as the state was taking another look -- millions across America were about to see the case too. These two people think you had something to do with their daughter's death. Reporter: There was Sheena's parents, Kelly and father Dave on the "Dr. Phil" show, and they were stunned because right there with them was Joe. So confident in his innocence he agrees to a polygraph test. Some would say, who would agree to go on a national TV show and take a polygraph test unless you're certain you're innocent? Exactly. Especially since the polygraphist that conducted the examination is one of the best in the country. He is the former chief polygraphist for the FBI's L.A. Field office. Maybe he thought that after four and a half years, he's been so convincing to all the authorities, that he'd be convincing there too. Reporter: He would have to convince them on two major points. The two questions were? Did he kill Sheena, or was involved somehow in her death? Reporter: And with millions watching, the results. The result on both questions is that that answer was deceptive. That you were not telling the truth. I literally became nauseous. How do you explain those test results? Well, I don't. I was uneasy with a lot of the questions he asked. Reporter: For the first time since being branded a liar on national television Joe genoese is speaking out. Sitting down with "20/20" saying far from a liar he's a victim too. So why sit down with me? Because I have to tell you my side of the story. I'm being victimized cause I cared about someone. Reporter: Put under the microscope he says by a mother determined to prove her daughter did not commit suicide. Joe says the portrait painted of his relationship with Sheena is not a true one. We've interviewed a lot of Sheena's friends. Many of her friends say that this was a tumultuous relationship. I just don't understand where they're getting at. There wasn't any fighting? Well, in a relationship, there's always -- there's always arguments and stuff. It was never physical? No you know, in a Normal relationship, there -- there was fights, there was, you know, back and forths. But there was no -- never any violence, no. Reporter: And he points out his fights with Sheena, including the one in that hotel room, were often caused by her jealousy of the children he already had. He says after a new year's kiss that night it was a call to his kids that set Sheena off. It lasted all about 15, 20 seconds that I was on the phone. And as I turned back around, she was right there. She just looked at me and said, "You just Up the whole night." Why did she have such a big problem with you calling your kids? She just didn't want me involved with my children. It was, like, another family to her. And she started getting really upset, screaming and yelling. And then she started punching the wall. Reporter: Joe says initially it was Sheena's idea to leave the hotel but she suddenly changed her mind -- refusing to go. She actually at one point tried to grab the money that I had on the bureau so -- and she said that I wasn't leaving. And I told her, "I am leaving. Because at that point, I -- you know, she -- from her punching the wall, and screaming and yellin' the way she did, I-- I was afraid that, you know, cops were gonna come. Reporter: But guests were already placing that call to 911. There's two people over there, just screaming and yelling, a woman and a man, at each other. Reporter: And Joe told us what police say he's always told them. And where did you go? Home. Straight home. Straight to my townhouse where there were people there, they were havin' a party, and at least five or six people saw me. Reporter: On the drive home, Joe says, Sheena was on the phone with him. Suddenly sounding desperate. What was she saying to you? There was one thing that she did say. In a somber note, she said, "If I can't have you all to myself, I don't wanna be here." Had she ever said that before? Not -- no. Reporter: As for that 911 call Sheena made just after 2:00 A.M. -- He just made me bleed and left claw marks all over me and stuff. The scrape on her -- on her finger, we know that came from her punching the wall. And the scrape on her neck when she went to grab the money off of the bureau, and -- I grabbed her by her -- her -- shirt, and -- and it -- and it got her necklace. And it left a little scratch on her neck. That's -- that's it. She said you had taken her purse, her house keys, her car keys -- No. That's not true. I didn't -- I wouldn't take her purse. I wasn't out to destroy anything. Reporter: And he says, like the mother who loved Sheena, he was devastated too that new year's day when they all learned she was dead. I walk up, and I -- and I -- and I look, and I asked, like, "What's going on?" He looked at me, he said, "I'm sorry for your loss." And I fell to my knees. And I just looked at him, and I couldn't believe what he said to me. Can we cut? Can we cut? Reporter: And when he was ready to continue. She was a beautiful girl. I -- this is a tragedy in everybody's lives, you know? For you too? Absolutely. I was engaged to her. Reporter: Do you think everybody's forgotten that you felt this way too? No, I just think that they -- they're on the Kelly train, and if you go against what Kelly says, then you're not an advocate of Sheena. And once and for all, did you kill Sheena? Absolutely not. Reporter: But that's just the question Florida's top investigators were working to answer.

This transcript has been automatically generated and may not be 100% accurate.

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